The proposed study aims to validate our experimental research on a novel and promising biomarker, humanin, a mitochondrial peptide encoded by mitochondrial DNA that has been previously shown to protect neurons from damage caused by Alzheimer's disease related proteins. We recently found that humanin also plays a role in the regulation of glucose metabolism in animals, by demonstrating the following - (i) Central administration of humanin improves insulin sensitivity as evidenced by significant decrease in hepatic glucose production and enhanced peripheral glucose uptake, leading to lowering of blood glucose and (ii) Peripheral administration of humanin can reproduce the central effects and also lead to significant enhancement in hepatic insulin action. We have also developed a highly sensitive ELISA assay to measure humanin in human plasma. Using this assay, we demonstrated that circulating humanin levels decrease with increasing age and are lower among those with diabetes compared to controls. Taken together, these data suggest that humanin may play an important role in the pathophysiology of several age-related diseases, including type 2 diabetes. Furthermore, our recent work demonstrated that humanin binds to IGFBP-3, a binding protein of insulin-like growth factor (IGF)-I. However, this link between humanin and IGF-axis has not been yet investigated in humans. The major aim of the current proposal is to prospectively evaluate the associations between baseline circulating levels of humanin and the risk of developing type 2 diabetes. In addition, we will investigate the relationship of humanin with measures of insulin secretion and sensitivity, the IGF-axis and several other biomarkers. Specifically, the proposed study will be conducted using already collected data and stored blood samples from the Diabetes Prevention Program (DPP), a well characterized population of individuals at high risk of diabetes (overweight/obese with impaired glucose tolerance) at baseline, which planned to evaluate the effect of lifestyle modification and metformin therapy in diabetes risk. The current study will build upon an existing nested case-control investigation (n=280 cases and 1:1 age and gender matched controls) within the placebo arm of the Diabetes Prevention Program (DPP). The relatively large sample size, validated data on the incident diabetes outcome, long-term follow- up and high quality covariate data are some of the advantages of this ancillary study. The study also provides a unique and cost-effective opportunity to investigate the relationship between humanin and several already measured biomarkers.